1. Field of the Invention
The present invention relates to an apparatus for dispensing beverages, for example, beer, and in particular, but not exclusively, to a beer tap for dispensing draught beer.
When dispensing beer in a bar or other point-of-sale location, the beer is commonly stored in a keg at a remote location from the point of dispense. A gas cylinder which contains carbon dioxide, or a mixture of nitrogen and carbon dioxide is connected with the keg and serves to keep the dissolved gasses in solution and can drive beer from the keg to the dispense tap.
In order to ensure that the beer is in the correct condition as it is supplied to the tap, it is common to pass it through a cooler and a pressure restrictor before it is delivered to the tap. In some installations, a pump is provided between the keg and the tap.
In conventional beer dispense systems, the tap is a simple on-off tap which is spring biased into its on and off positions. Prior to use, the dispense system is set up with the intention that the beer is dispensed at the correct rate and in the correct condition when the tap is fully open. Conventional taps have a simple plug valve member which is moved into and out of engagement with a valve seat through which the beer flows. Downstream of the valve is a nozzle normally of uniform internal bore to bring the flow into a continuous stream. The intrinsic design of these valves does not readily allow controlled break out of gas from beer and, hence the extent of beer head formation may be variable.
A generic tap of the type described above which is used by pubs and bars for dispensing draught beer is (schematically illustrated in the schematic representation) shown in FIGS. 1 and 2. The tap comprises an inlet pipe 1 which opens into a cylindrical chamber 2. A valve head 3 is centrally located in the chamber and is arranged to close against a valve seat 4 which is formed on the upper end of a depending dispensing spout 5. The diameter of the valve head 3 is significantly less than the internal diameter of the chamber 2 so that beer may flow around all sides of the valve head to reach the dispensing spout 5. Thus, in use the beer flows into the tap through the inlet pipe, flows against the valve head 3 and then down through the dispensing spout. As can be seen from FIGS. 1 and 2, on impacting the valve head, some beer will flow in either direction around the head.
The inventors have recognized that this flow pattern gives rise to turbulence and stagnation points within the chamber 2, particularly in the region opposite the inlet pipe. This causes flow energy to be used up and thus a relatively large pressure drop is produced across the tap.
Thus, the beer in the kegs must be provided at a sufficiently high pressure to allow for this pressure drop.
In addition, the flow through the taps may have a detrimental effect on the quality of the beer being dispensed because the transition of the beer from an unsaturated to a supersaturated state may occur within the tap itself.
It is often important that beer be dispensed with an attractive head of foam. The head on draught beer is known to be produced from the breakout or separation of gas in the beer to produce bubbles and a xe2x80x9ctightxe2x80x9d creamy head formed of small bubbles is usually considered most desirable.
Beers currently marketed are generally of one of two types; ales typically containing 1.1-1.7% vol/vol of dissolved carbon dioxide and often 15-55 mg.lxe2x88x921 of dissolved nitrogen, or lagers containing 2.0-2.8% vol/vol of dissolved carbon dioxide. In either case, the beer enters the glass as a supersaturated solution which means that the dissolved gas it contains has the potential to break out of solution. The extent to which this occurs depends on a number of factors. These include the level of supersaturation, the flow conditions and the existence of nucleation sites to initiate bubble growth. During beer dispense, the generation of gas bubbles in solution originates predominantly by heterogeneous bubble nucleation. This means that bubbles are either nucleated at a surface containing pre-existing nucleation sites or in solution as a consequence of air being entrained in the beer as it flows into the glass.
2. Discussion of the Related Art
Many different methods have been tried in the past to produce a high quality head on draught beer. For example, nitrogen may be added to the beer and also a flow restrictor is usually provided in the base of the dispensing tap.
Such flow restrictors traditionally are flat discs containing five holes each having a diameter of from 0.5 to 1 mm. The decreased flow aperture provided by the holes causes a pressure drop across the flow restrictor producing gas breakout and the formation of a head on the beer.
However, the problem with these known taps having flow restrictors is that a high pressure drop occurs across the flow restrictor itself which can lead to a loss of control of head formation.
Viewed from a first aspect, the present invention provides a beverage dispensing apparatus, the apparatus being formed so as in use to provide a vortexial motion in the mass of beverage flowing through the apparatus.
The vortexial motion of the invention in the mass (i.e. the bulk) of the beverage is to be distinguished from the existence of localised vortices or eddies which occur in the turbulent-flow in disperse taps. However, it should be understood that the flow within the vortex will itself typically be turbulent.
In the vortexial flow of the invention, a low pressure area is produced at the center of the vortex so that the pressure in that region falls below equilibrium pressure and thus results in gas separating out from the liquid beverage. Since the gas breakout is achieved without the need for a flow restrictor, the pressure drop associated with these devices does not occur. Consequently the beverage may enter the apparatus at a lower pressure. Moreover it has been found that a high quality head is formed on the draught beverage dispensed from the apparatus of the invention.
It has been found particularly effective to provide the apparatus with a flow chamber having a substantially circular cross section in which the vortexial motion is induced together with an inlet leading to that chamber and an outlet leading therefrom.
A particularly effective way to induce the vortexial motion in such a chamber is for the inlet to extend substantially at a tangent to the circular cross section of the flow chamber. In this way, beverage flowing into the apparatus flows into the chamber from the inlet and along the inner face of its side wall. Thus the beverage flows around the chamber and thereby sets up a vortexial flow.
While it is possible to vary the direction of the flow of beverage relative to the flow chamber, preferably the beverage inlet comprises a conduit which extends substantially perpendicular to the longitudinal axis of the flow chamber so that the flow path of the beverage forms a tangent to the flow chamber, as previously discussed. Preferably the inlet conduct is also substantially horizontal.
Although the action of the beverage flowing around the walls of the flow chamber is sufficient to cause a vortex motion, it is significantly essential to have a vortex finder within the flow chamber aligned in relation to the beverage inlet such that, in use, beverage flowing into the flow chamber is guided in a circular path between the outer surface of the vortex finder and the inner wall of the flow chamber. Thus, with a vortex finder provided as described above, the beer flowing through the apparatus is encouraged to flow cyclically around the flow chamber.
The vortex finder could be of any form which provides the required flow pattern. Preferably however, the vortex finder comprises a portion in the form of a cylinder.
Still more preferably, the vortex finder further comprises a conic or frusto-conic part provided at the downstream end thereof (i.e. the end closer to the outlet). This further encourages the beverage to retain its vortex flow.
Since draught beverages are kept under pressure which propels the beverage through the dispensing system, the apparatus of the invention could be arranged in any orientation. Indeed, it could be provided as a mobile, hand held device. However, it is usually most convenient to dispense beverages from a generally vertical outlet e.g. fastened to a counter. It is therefore preferred that the flow chamber comprises an upstream portion defining a vortex finding chamber in which the vortex finder is located and a downstream portion depending from the upstream portion which preferably comprises a conic or frusto-conic part. In use the apparatus may be arranged substantially vertically such that the beverage flows helically downwardly through the downstream portion of the flow chamber assisted by the action of gravity and is dispensed through the outlet.
The flow chamber could be of any form which allowed vortexial flow to form and be maintained. For example, it could be in the form of a hollow cylinder. However, preferably the flow chamber is formed to enhance the vortex generating effect, for example by providing it with a main body having a circular cross section wherein at least the downstream portion thereof decreases in diameter along its axis in the downstream flow direction.
When the tap is formed as described above, the vortexial flow of the beverage will be accelerated as it flows towards the distal end of the flow chamber. This results in a gradually increasing radial pressure drop which increases gas breakout and thus improves the quality of the head which is formed.
The beverage could in use be allowed to flow directly out of the flow chamber. However, beverage flowing out without any further guidance may form a triangulated or cone shape. Thus preferably, a vortex breaker is provided, ideally in the downstream portion, near the exit point. Similar devices are well known in the art as flow directors. These enable beverage to flow out of the apparatus in a smooth straight column without significantly restricting its flow.
The invention in its simpler forms may be used in conjunction with an associated flow control such as a valve or tap provided upstream. However, it is particularly preferred for the flow control to be formed integrally such that there is provided a tap which may be used as a direct replacement of the prior art taps previously discussed.
An especially convenient way of achieving this objective is for the previously described vortex finder to be in the form of a valve head which acts in co-operation with the surfaces of the flow chamber and/or the outlet tube to control the flow of beverage through the apparatus.
Although the diameter of the flow chamber cross section could decrease evenly along its axis in the downstream flow direction, particularly when providing a vortex finder on the valve head, it is preferable that the vortex finding chamber defined by the upper portion of the flow chamber has a constant cross sectional diameter, i.e. be in the form of a hollow cylinder. This simplifies the design and manufacture of the valve head. The cross sectional diameter of the downstream portion of the flow chamber may then reduce in the downstream direction of flow as described above.
Since this valve arrangement is such that the beverage flows around the vortex finder (which forms the valve head) in a single direction in order to produce the vortex flow, it follows that the stagnation points associated with the prior art taps are significantly reduced if not eliminated. Consequently, there is a much smaller pressure drop across the valve which means that the pressure under which the beverage is kept may be further reduced.
This valve arrangement is, in itself, believed to be inventive and therefore, viewed from a second aspect, the invention provides a beverage dispensing tap comprising an inlet conduit, a flow directing chamber, a valve member located within the flow directing chamber and an outlet conduit leading from the flow directing chamber, wherein the inlet conduit is arranged in relation to the flow directing chamber such that beverage flowing into the tap is directed to flow around the valve member substantially in one direction.
Since this arrangement significantly reduces the pressure drop across the valve, it may be useful in many types of dispensing apparatus. However, it is particularly advantageous for the tap to be provided with the preferred features discussed above. In particular, the outlet conduit preferably depends from the flow directing chamber and is arranged such that the flow of beverage around the valve member establishes a vortexial flow within the outlet conduit.
The flow directing chamber may preferably be at least substantially cylindrical. However it is possible that conical or frusto-conical chambers could be developed in which case the valve member will preferably be similar such that a flow passage with concentric sides is formed.
The valve member may act against a valve seat formed at the upstream end of the outlet conduit. However, this may interfere with the desired vortexial flow and so it is preferred for the valve member to be provided with a portion arranged to close the flow path from the inlet to the flow directing chamber. The valve member should preferably be designed so as to open and close the flow path rapidly to avoid turbulence and gas breakout caused by a partially open flow path. This may, for example, be achieved by providing the valve member with a vortex finder portion having a diameter significantly less than that of the flow directing chamber and a valve portion having a diameter substantially the same as the inside diameter of the flow directing chamber, the valve member being axially movable within the flow directing chamber in such a way that the valve portion opens and closes the inlet conduit.
Alternatively, the flow path may be opened and closed by rotary motion of the valve member. This may be achieved by providing the valve member with a vortex finding portion having a diameter significantly less than the flow directing chamber and a circumferential wall portion located radially outward of the vortex finding portion and having a diameter substantially corresponding to that of the flow directing chamber, wherein an inlet port is provided in the circumferential wall portion and the valve member is rotatable within the flow directing chamber to bring the inlet conduit into and out of registration with the inlet port in such a way that the valve portion opens and closes the inlet conduit. The components could be made to sufficiently close tolerances to be self-sealing, but preferably a suitable sealing material is provided around the valve portion.
The apparatus of the invention could be made of any suitable material. Such materials include for example materials having a smooth surface such that nucleation sites upon which bubbles can grow and break out are not provided such as glass or plastics. Possible plastics material for construction of the tap are polymethyl methacrylate or nylon but, it is preferred that acetal be used since it is easily moldable to give a smooth finish and has a low moisture absorption characteristic and is a safe material to use in conjunction with a food product. In another preferred form, the tap is made of a corrosion resistant metal such as stainless steel having a smooth internal finish.
The apparatus of the invention could have a taper angle of the frusto-conic portion of up to about 45xc2x0. Preferably however, the conic or frusto-conic part of the apparatus has a taper angle of less than 30xc2x0. Still more preferably, the conic or frusto-conic part thereof has a taper angle of less than 15xc2x0 or 10xc2x0 or 7xc2x0. Yet more preferably, the conic or frusto-conic part thereof has a taper angle of between 7xc2x0 and 3xc2x0. Optimum performance of the apparatus has been shown to be achieved with a taper angle of at least about 5xc2x0 and still more preferably, the conic or frusto-conic part thereof has a taper angle of 5xc2x0. All of the above taper angles are defined relative to the longitudinal axis of the beverage dispensing apparatus.
It is envisaged that the dimensions of the apparatus of the invention could be chosen within a wide range. Preferably however, the conic or frusto-conic part thereof has a height of between 100 mm and 30 mm. Optimum performance of apparatus according to the invention has shown to be achieved within a narrower range of dimensions however and so, more preferably, the conic or frusto-conic part thereof has a height of 40 mm to 60 mm, e.g. about 50 mm.
The invention also provides a novel and improved way of dispensing a beverage and so, from a third aspect, the present invention provides a method of dispensing a draught beverage by forming a vortexial flow in the mass of the beverage as it is dispensed. According to a still further aspect of the invention there is provided a method of dispensing a beverage comprising supplying the beverage to a flow directing chamber having a valve member located therein such that the beverage flows around the valve member substantially in one direction before flowing out of the chamber and being dispensed.
Preferably the methods are performed using an apparatus as previously described.